Add initial version of IndependentSampler

Also add randFloat32() function to work around a bug in
math.rand.Rand.Float32().
Add scaffolding for RadianceMeter
Flesh out Spectrum and RadianceMeter
Add scaffolding for PathTracer
Flesh out Ray
Add scaffolding for PathTracer.ComputeLi()
Add PrimitiveList
Add GeometricPrimitive and more scaffolding
Add Sphere and more scaffolding
Add Diffuse material
Use hollow sphere test scene

Feature-End: initial-scene
Fill out Ray

Feature-Start: cosine-weighting
Implement cosine-weighted hemisphere sampling

Feature-End: cosine-weighting
Build the renderer from a config map

Feature-Start: read-config
Build the scene from a config map

Also add comments about hollow sphere scene.
Read config from file

Feature-End: read-config
Communicate sample range from sensor to sampler

Feature-Start: multiple-sensors
Make sensors part of the scene

Add GetSensors() function to Primitive.

Add PointPrimitive.

Add "black" Spectrum type.
Add hollow sphere with center light example

Feature-End: multiple-sensors
Add Cornell box example

Feature-Start: perspective-camera